Needle holder for fluid collection and/or injection system

ABSTRACT

A needle holder for use with a fluid transfer system of the type having a standard threaded cannula and a fluid container. The needle holder includes an actuation mechanism for detachably mounting a cannula to the holder, the actuation mechanism including pivotable threaded halves and an actuator operably associated therewith. In a cannula-mounting position, facing surfaces on the threaded halves cooperate to define a threaded passageway for engaging the cannula. Upon operation of the actuator, the threaded halves pivot to a retracted position to disengage from the cannula.

This application is a continuation of application Ser. No. 08/580,322filed on Dec. 28, 1995, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to the manipulation of devices throughwhich fluids are delivered to and/or withdrawn from an animal throughvenipuncture. More particularly, this invention is directed to a holderfor use with a fluid collection and/or injection system of the typeincluding a double ended needle assembly and associated fluid containerand, specifically, to such a holder having an actuation mechanism forselectively mounting or detaching the needle assembly. Accordingly, thegeneral objects of the present invention are to provide novel andimproved methods and apparatus of such character.

2. Description of the Related Art

While not limited thereto in its utility, the present invention isparticularly well suited for use in fluid transfer systems of the typewhich are used to inject fluids into and to draw blood specimens from apatient. Current medical practice requires that the fluid containers andneedle assemblies used in such systems be inexpensive and readilydisposable. Consequently, existing blood collection systems, forexample, typically employ some form of durable, reusable holder on whichdetachable and disposable needles and fluid collection tubes may bemounted. A blood collection system of this nature can be assembled priorto use and then disassembled after usage. Thus, these blood collectionsystems allow repeated use of the relatively expensive holder uponreplacement of the relatively inexpensive disposable needle and/or fluidcollection tube. In addition to reducing the cost of collecting bloodspecimens, these blood collection systems also help minimize theproduction of hazardous medical waste.

The most popular design configuration of previously available bloodcollection systems includes a double ended needle assembly, an evacuatedcollection tube, and a holder for maintaining the needle assembly andthe collection tube in fixed relation. The double ended needle assembly,which is also referred to as a cannula, has a bore extendingtherethrough and a hub near a central region thereof. The evacuatedfluid collection tube includes a puncturable stopper at one end thereof.In this type of blood collection system, the holder typically has ahousing at one end thereof for receiving the needle assembly. Likewise,the holder also has a hollow body with an opening at an opposite endthereof for receiving the collection tube. The needle assembly isrigidly received within the housing of the holder such that a first endof the needle extends forwardly of the holder for puncturing the vein ofa patient. The opposite, second end of the needle extends into thehollow body of the holder. Upon assembly of the blood collection system,the needle assembly is inserted into the housing and the collection tubeis inserted through the open end of the hollow body until the second endof the needle pierces the puncturable stopper of the collection tube,thereby allowing fluid communication between the interior of thecollection tube and the bore which extends through the needle assembly.To draw a blood specimen from a patient using one of these bloodcollection systems, the evacuated collection tube is partially insertedinto one end of the holder, the first end of the needle is inserted intoa patient's vein and the collection tube is fully inserted into theholder such that blood will be drawn through the bore of the needleassembly and into the fluid collection tube. After drawing the specimen,the collection tube is removed so that the blood contained therein canbe analyzed and the needle assembly is detached for disposal. Inaddition to being capable of accommodating blood collection tubes, theholders of some prior art fluid transfer systems are compatible withfluid containers having a fluid to be injected into a patient. Thus,such holders can be used to inject fluid into, as well as draw bloodspecimens from, a patient. Efforts to improve prior art fluid transfersystems of the type briefly described above have largely focused onimproving the mechanism for removably mounting the needle assembly tothe holder.

One early, and extremely popular, type of mechanism for removablymounting a needle assembly to a holder utilized a fixed threadedpassageway at one end of the holder designed to threadably receivecomplementary threads on the hub of the needle assembly. With a holderof this type, a threaded cannula could be screwed into position prior todrawing a blood specimen from a patient, subsequently unscrewed from theholder and discarded.

Blood collection systems employing a holder with a fixed threadedpassageway, however, suffer from a number of serious deficiencies. Themost serious of these deficiencies stems from the need for the healthcare worker to physically handle the cannula after it has been incontact with the patient's blood in order to unscrew the threadedcannula from the holder. This handling typically entails placing aprotective cap on the externally extending portion of the threadedcannula, twisting the threaded cannula to free it from the fixedthreaded passageway of the holder, and disposing of the used cannula.Thus, removal of the needle from a blood collection device of this typeinevitably gives rise to the possibility of accidental contact betweenthe health care worker and the patient's blood. Another deficiency ofthe above-described arrangement resides in the relatively long period oftime it takes a health care worker to remove the needle from the holder.Nonetheless, due to widespread usage of this type of blood collectionsystem, health care workers have now become accustomed to using threadedcannulas.

In response to the above-mentioned deficiencies of fixed threadedpassageway holders, holders have recently been developed which employunthreaded needle-locking mechanisms with a remote release element forejecting the needle assembly from the needle-locking mechanism. Thistype of arrangement has generally been considered to be a functionalimprovement over fixed threaded passageway holders because, by operatingthe release element, a health care worker may quickly remove a needleassembly from a holder without the need to physically contact anyportion of the needle assembly directly. This reduces the risk that thehealth care worker will accidentally contact the patient's blood. Todate, however, most of the blood collection devices with holders havingreleasable needle-locking mechanisms have been incompatible with whathas now become the industry standard threaded cannula, i.e., a doubleneedle assembly with a threaded hub in a central region thereof and ahub disk located at one end of the threaded portion of the hub. Thus,most of these recently developed holders have required the use ofrelatively expensive, custom designed needle assemblies.

Holders having a needle ejection feature which are compatible with thestandard double needle configuration have also been developed. However,these holders have either suffered from overall poor performance and/orhave required the use of a separate adapter, for accommodating astandard threaded cannula, which is discarded along with the cannulaupon removal of the cannula from the holder. In addition to increasingthe overall cost of the blood collection system, the use of such anadapter can also unnecessarily complicate assembly and/or disassembly ofthe blood collection system.

In light of the foregoing, there exists a need in the health careindustry for a needle holder for use with a fluid transfer system which(1) is compatible with standard threaded cannulas; (2) allows a user todetach a threaded cannula from the holder without physically handlingany portion of the threaded cannula; and (3) is capable of operatingeffectively without the need for any additional components.

SUMMARY OF THE INVENTION

The present invention satisfies the above needs, and overcomes theabove-stated and other deficiencies of the prior art, by providing aholder having a cannula actuation mechanism within a housing at one endof the holder for removably mounting an externally threaded cannulathereto. The actuation mechanism includes first and second mountingjaws, which may comprise first and second threaded halves with surfaceswhich cooperate to define a threaded passageway therebetween when thethreaded halves are in a cannula-mounting position. At least one of thethreaded halves is mounted within the housing in such a manner as toallow movement thereof from the cannula-mounting position to a retractedposition wherein the threaded surfaces define a gap which is appreciablygreater than the maximum cross-section of the cannula hub. The actuationmechanism also includes an actuator with at least one structural portionfor normally maintaining the threaded halves in the cannula-mountingposition. The actuator is slidably mounted to the holder and operablyassociated with the threaded halves such that, upon user-operation ofthe actuator, at least one of the threaded halves moves to the retractedposition. To removably mount a standard double ended cannula to a holderin accordance with the present invention, a user simply inserts astandard threaded cannula, with its protective cap in place, into theholder and screws the threads of the cannula hub into the threadedpassageway defined by the threaded surfaces of the threaded halves untilthe hub disk of the cannula hub abuts the top surfaces of the threadedhalves. To release a threaded cannula from a holder in accordance withthe present invention, the user simply orients the holder over a “sharpsdisposal box” such that the first end of the cannula extends verticallybelow the holder, and depresses the actuator to retract the threadedhalves thereby allowing the cannula to fall from the holder under theforce of gravity.

The cannula holder of the present invention is wholly compatible withstandard threaded cannulas. This compatibility is achieved by pivotablymounting at least one of the threaded halves of the actuation mechanismwithin a housing located at one end of the holder. When these threadedhalves are in the cannula-mounting position, a standard threaded cannulacan be threaded into the threaded passageway in the same manner as astandard threaded needle assembly would be threaded into a holder havinga fixed threaded passageway. However, upon user-operation of anactuator, which is located on the holder in a position where it isunlikely to be contaminated, at least one of the threaded halves pivotsapart to a retracted position, thereby detaching the threaded cannulafrom the actuation mechanism. Thus, the present invention is compatiblewith standard threaded needle assemblies and can be used by health careworkers in a manner substantially similar to the prior art needleholders to which they are accustomed.

Another significant advantage of the present invention when compared topreviously available needle holders with an ejection capability isreduced cost. Since the present invention is wholly compatible with bothstandard threaded cannulas and standard fluid collection tubes, holdersin accordance with the present invention do not require the use ofexpensive custom made cannulas and/or additional custom made components.

Yet another advantage of the invention relative to previously availablefluid collection devices is improved reliability and ease of operation.To assemble a fluid transfer device using a holder in accordance withthe present invention, a user simply threads a standard cannula into theactuation mechanism at one end of the holder and inserts a fluidcontainer into an opening at the opposite end of the holder. After use,the fluid container is removed from the holder, the holder is positionedover a “sharps disposal box”, and the actuator is depressed therebyretracting the threaded halves of the holder and allowing the cannula tofall into the “sharps disposal box” under the force of gravity. Thisassembly procedure is identical to the assembly procedure used withconventional prior art holders. The disassembly procedure, on the otherhand, avoids the need to unscrew a cannula, twist a bayonet mechanism orflip a lever as was necessary with various prior art holders.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described below with reference to theaccompanying drawings, wherein like reference numerals represent likeelements in the several figures, and wherein:

FIG. 1 is a perspective view of one embodiment of a holder in accordancewith the present invention shown in combination with a standard threadedcannula and a standard fluid collection tube;

FIG. 2 is an exploded perspective view of the holder shown in FIG. 1;

FIG. 3a is a cross-sectional view of the holder shown in FIGS. 1 and 2,illustrating the actuation mechanism in a cannula-mounting position;

FIG. 3b is a view similar to FIG. 3a, illustrating the actuationmechanism in the retracted position;

FIG. 4a is a fragmentary medial sectional view, taken along thelongitudinal axis, of the holder of FIGS. 1 and 2 shown in combinationwith a cannula; FIG. 4a illustrating the actuation mechanism in thecannula-mounting position; and

FIG. 4b is a fragmentary, medial sectional view, taken along thelongitudinal axis, of the holder of FIGS. 1 and 2 shown in combinationwith a cannula; FIG. 4b illustrating the actuation mechanism in theretracted position.

DESCRIPTION OF THE DISCLOSED EMBODIMENT

With reference to the drawings, FIG. 1 shows a perspective view of aholder 10 in accordance with the present invention in combination with astandard threaded cannula 40 and a standard collection tube 50. Holder10 generally consists of a hollow body 14, a housing 11 having an endcap 60 at one end thereof, and an actuation mechanism 20. Body 14 ofholder 10 defines a longitudinal axis 5. Threaded cannula 40 is shown inaxial alignment with axis 5 for insertion into actuation mechanism 20.Threaded cannula 40 has a first end 42, a second end 43, and a threadedhub, indicated generally at 45, intermediate the ends. A longitudinalbore 44 extends along the length of cannula 40. Hub 45 of threadedcannula 40 includes a threaded portion 48 which terminates, at one endthereof, at a hub disk 46. When cannula 40 is mounted on holder 10, thefirst end 42 extends forwardly of holder 10 and the second end 43extends into hollow body 14.

Collection tube 50, when the system is assembled and in use, will alsobe in axial alignment with hollow body 14 of holder 10 and will bereceived therein. Collection tube 50, in the disclosed embodiment, is astandard evacuated blood specimen collection tube which consists of anelongated tube 52 having a rubber stopper 54 at one end thereof. Therubber stopper 54 has a puncturable membrane 56 in a central region ofthe stopper 54. Upon insertion of collection tube 50 into the hollowregion of hollow body 14, second end 43 of threaded cannula 40 piercesmembrane 56 and extends into the interior of tube 52. Thus, when thefluid transfer system is fully assembled, bore 44 of cannula 40 is influid communication with the interior of collection tube 50 and thesystem can be used to draw a blood specimen from a patient.Alternatively, the present invention may be used to inject a fluid intoa patient using a fluid container with a piston for injection of a fluidinto a patient. First and second grip tabs 19 and 19′ on holder 10assist insertion of collection tube 50, or other fluid container, intoholder 10.

With primary reference now to FIG. 2, the various components of holder10 will be described in greater detail. As shown in FIG. 2, actuationmechanism 20 generally consists of a spring biased actuator, indicatedgenerally at 30, a pivot axle 21 and first and second threaded halves 22and 22′, respectively. Housing 11 includes a bearing wall 39, the endcap 60, sidewalls 18 and 18′ and end walls 15 and 15′ (see FIGS. 3a and3b). While bearing wall 39 and pivot axle 21 are preferably integrallyformed with an end wall 16 of hollow body 14, threaded halves 22 and22′, and actuator 30, are movably mounted to housing 11. Actuationmechanism 20 is captured within housing 11 between end wall 16 and endcap 60. As shown in FIG. 2, threaded halves 22 and 22′ preferablyinclude apertured collars 25 and 25′ which are pivotably mounted withinhousing 11 via engagement with pivot axle 21. Alternatively, each ofthreaded halves 22 and 22′ can be pivotably mounted within housing 11for rotation about separate pivot axles. Threaded halves 22 and 22′ alsoinclude first and second threaded surfaces 24 and 24′, respectively,which generally face one another and which cooperate to define athreaded passageway 23 (see FIG. 3a) having a substantially circularcross-section when biased to the position shown in FIGS. 3a and 4a.First and second threaded halves 22 and 22′ further includesubstantially planar first and second top surfaces 28 and 28′,respectively, located substantially perpendicularly to threaded surfaces24 and 24′. First and second torque members 26 and 26′ extend fromcollars 25 and 25′, respectively, and define torque arms for drivingthreaded halves 22 and 22′ in respective first directions about pivotaxle 21. Actuator 30 is generally in the form of a user-operablepush-button which is operably associated with first and second threadedhalves 22 and 22′. Actuator 30 generally consists of an external element38, first and second driver arms 32 and 32′ extending therefrom,resilient fingers 36 and 36′, and a stop member 35. Additionally, driveprojections 34 and 34′, respectively, extend from the free ends of arms32 and 32′ for engagement with respective torque members 26 and 26′.

As shown in FIG. 2, substantially planar end cap 60 has an extendedportion 64 at one end thereof, a recess 63 at an opposite end thereof,and an aperture 62 therebetween. Upon assembly of holder 10, end cap 60serves to retain most of actuator 30 and first and second threadedhalves 22 and 22′ within housing 11. To secure end cap 60 to holder 10,end cap 60 preferably engages sidewalls 18 and 18′ of housing 11 atbeveled regions 65 and 67 and a lip on bearing wall 39 at a beveledregion 66. Additionally, recess 63 of end cap 60 preferably engagespivot axle 21 in snap-fit fashion to prevent end cap 60 from slidingfrom holder 10. As an alternative, end cap 60 may be secured to holder10 with many other well known fixation means such as adhesive bonding,affixation with fasteners or any equivalent thereof. When holder 10 isassembled, aperture 62 of end cap 60, aperture 17 of end wall 16 andthreaded passageway 23 defined between threaded surfaces 24 and 24′ aregenerally coaxial. This relationship defines a continuous passagewaythrough which a threaded cannula 40 may pass upon insertion thereof intoholder 10.

The operation of the various components of actuation mechanism 20 willnow be described with joint reference to FIGS. 3a and 3b. FIG. 3a showsa cross sectional view of the holder of FIGS. 1 and 2 illustratingactuation mechanism 20 in the cannula-mounting position. When actuationmechanism 20 is in this position, actuator 30 is urged radially outwardwith respect to housing 11 by the cooperation of resilient fingers 36and 36′ and bearing wall 39. In this position of actuator 30, externalportion 38 thereof is substantially aligned with grip tab 19 and (FIG.2) extended portion 64 of end cap 60. Furthermore, shoulders on driveprojections 34 and 34′ contact exterior surfaces of threaded halves 22and 22′ and arms 32 and 32′, respectively, contact side walls 18 and 18′of housing 11 to constrain threaded halves 22 and 22′ from pivotingapart. Thus, in the cannula-mounting position, cooperation between driveprojections 34 and 34′ and threaded halves 22 and 22′, ensuresmaintenance of a rigid threaded passageway 23 between facing threadedsurfaces 24 and 24′.

The movement of actuation mechanism 20 from the cannula-mountingposition into the retracted position occurs upon user-operation ofactuator 30. As described above, external element 38 of actuator 30extends radially outwardly from holder 10 when actuation mechanism 20 isin the cannula-mounting position. Upon depression of external element 38of actuator 30 in the direction of arrow 7 (see FIG. 3b), arms 32 and32′ cooperate with side walls 18 and 18′ to guide actuator 30 linearlyin the direction of arrow 7. Upon partial depression of external element38, drive projections 34 and 34′ temporarily disengage from threadedhalves 22 and 22′. Thus, threaded halves 22 and 22′ are no longerconstrained from rotation about pivot axle 21. Upon further depressionof external element 38, drive projections 34 and 34′ engage torquemembers 26 and 26′ to urge threaded halves 22 and 22′ to pivot inopposite directions about pivot axle 21 from the cannula-mountingposition to the retracted position shown in FIG. 3b. Simultaneously withdepression of external element 38, resilient fingers 36 and 36′ are bentinwardly and the outer surface of external element 38 becomes generallyflush with the outer surface of holder 10. When actuator 30 is fullydepressed, torque members 26 and 26′ are pinched between end walls 15and 15′ of housing 11 and drive projections 34 and 34′ of actuator 30.Additionally, resilient fingers 36 and 36′ are pinched between bearingwall 39 and stop member 35 of actuator 30. Upon release of actuator 30,resilient fingers 36 and 36′ and bearing wall 39 cooperate to urgeactuator 30 to slide back to its initial position along a linear path ina direction opposite to that of arrow 7. During return of actuator 30 toits initial position, drive projections 34 and 34′, once again,cooperate with threaded halves 22 and 22′ to return threaded halves 22and 22′ to the cannula-mounting position. Optionally, a number ofoperationally equivalent structures can be used to pivot threaded halves22 and 22′ between the cannula-mounting and retracted positions. Forexample, at least one of torque members 26 and 26′ can be positioned ontop surfaces 28 and 28′ of threaded halves 22 and 22′, for engagementwith at least one camming channel on actuator 30. An additional optionincludes providing threaded engagement between the various components ofthe actuation mechanism 20 such as between torque members 26 and 26′ andactuator 30.

The cooperation between actuation mechanism 20 and threaded cannula 40will now be described in greater detail with reference to FIGS. 4a and4b. FIG. 4a depicts a cross-sectional view of holder 10 illustratingactuation mechanism 20 in the cannula-mounting position in combinationwith cannula 40. As shown therein, when threaded cannula 40 has beenfully threaded into threaded passageway 23 of holder 10, threads 48 ofcannula hub 45 engage threaded surfaces 24 and 24′ of threaded halves 22and 22′. Additionally, hub disk 46 of cannula hub 45 abuts top surfaces28 and 28′ to prevent further rotation of cannula 40. Since aperture 62of end cap 60 and aperture 17 of end wall 16 are both appreciably largerthan threaded passageway 23, the only contact between holder 10 andcannula 40 occurs between threads 48 and threaded surfaces 24 and 24′,and between hub disk 46 and top surfaces 28 and 28′. Limiting contactbetween holder 10 and cannula 40 in this way helps ensure effectiveremoval of cannula 40 from actuation mechanism 20 upon retraction ofthreaded halves 22 and 22′.

Referring now to FIG. 4b, actuation mechanism 20 is shown therein withthreaded halves 22 and 22′ in the retracted position and threadedcannula 40 aligned with, but detached from, actuation mechanism 20. Asillustrated in FIG. 4b, the substantially thinner driver arms 32 and 32′of actuator 30 are generally aligned with threaded halves 22 and 22′ toallow threaded halves 22 and 22′ to retract away from one another. Alsoas shown, when threaded halves 22 and 22′ are in the retracted position,threaded surfaces 24 and 24′ no longer define a threaded passageway.Since threaded surfaces 24 and 24′ are now generally aligned with theperimeters of apertures 62 and 17, threaded cannula 40 is detached fromactuation mechanism 20. Thus, if holder 10 is oriented vertically,cannula 40 is free to fall from holder 10 under the force of gravity andholder 10 can be subsequently reused. The various components of holder10 can be made from a wide variety of materials. In one reduction topractice, hollow body 14, housing 11, bearing wall 39 and pivot axle 21are integrally formed from inexpensive, moldable plastic. Additionally,in this embodiment first and second threaded halves 22 and 22′ and endcap 60 are also individually formed of inexpensive plastic. The actuator30, however, is preferably made from an acetal, or equivalents thereof,because of its resilience, its durability and its low coefficient offriction. These properties enable resilient fingers 36 and 36′ toprovide sufficient biasing force against movement of actuator 30 whilestill allowing actuator 30 to freely glide against sidewalls 18 and 18′when depressed.

While a preferred embodiment of the present invention has beenillustrated and described in detail, it should be readily appreciatedthat many modifications and changes thereto are within the ability ofthose of ordinary skill in the art. Therefore, the appended claims areintended to cover any and all of such modifications which fall withinthe true spirit and scope of the invention.

What is claimed is:
 1. A needle holder for use with a fluid collection and/or injection system of the type having a double-ended cannula and a fluid container, the cannula including a fluid passage bore extending therethrough and a generally cylindrical, externally threaded hub with a hub disk at one end thereof, the fluid container including a sealed open end and an opposing closed end, said needle holder comprising: a hollow body having an end wall at a closed first end thereof, said end wall having an aperture therethrough, said hollow body also having an open second end disposed opposite to said first end for receiving a fluid container within said hollow body such that, upon reception of the fluid container, the open end of the fluid container is adjacent to said end wall; housing means abutting said first end of said hollow body for maintaining at least a portion of an actuation mechanism within said holder, said housing means including means defining an aperture therethrough which is generally coaxial with said aperture of said end wall; and an actuation mechanism for threadably mounting a threaded cannula hub therein with one end of the cannula extending forwardly of said actuation mechanism for venipuncture and the other end extending rearwardly into said hollow body for engagement with the fluid container, said actuation mechanism including: first and second threaded halves mounted within said housing means for removably mounting the cannula hub upon threading the cannula hub into said actuation mechanism, each of said threaded halves including a threaded surface, at least one of said first and second threaded halves being movable between a cannula-mounting position wherein said threaded surfaces cooperate to define a threaded passageway complementary in cross-sectional shape to the cross-sectional shape of the threaded cannula hub, and a retracted position wherein said threaded surfaces cooperate to define an opening having a cross-sectional size which is greater than the cross-sectional size of the threaded cannula hub; means for movably mounting at least one of said first and second threaded halves within said housing means; and actuation means for urging at least one of said first and second threaded halves between said cannula-mounting and retracted positions, said actuation means being slidably mounted to said housing means for movement between an initial position wherein at least one of said first and second threaded halves is urged into said cannula-mounting position, and a secondary position wherein at least one of said first and second threaded halves is urged into said retracted position.
 2. The needle holder of claim 1 wherein said at least one of said first and second threaded halves is pivotable between the cannula-mounting position and the retracted position, and said means for movably mounting at least one of said first and second threaded halves within said housing means comprises means for pivotably mounting said at least one of said first and second threaded halves.
 3. The needle holder of claim 2, wherein at least one of said first and second threaded halves further comprises a torque member; and wherein said actuation means includes: a user-operable external element; and at least one drive arm extending from said actuation means, said drive arms engaging said torque members to urge at least one of said first and second threaded halves into said retracted position in response to the application of linear force to said user-operable external element.
 4. The needle holder of claim 1 or claim 3, wherein said actuation means further comprises: resilient means for biasing said actuation means to said initial position wherein at least one of said first and second threaded halves is urged into said cannula-mounting position by said drive arms of said actuation means.
 5. The needle holder of claim 4, wherein said housing means further comprises: a bearing wall for opposing said resilient means of said actuation means; and an end cap at one end of said holder for maintaining at least a portion of said actuation mechanism within said housing means, wherein said end cap includes said means defining an aperture in said housing means.
 6. The needle holder of claim 5, wherein said end cap of said housing means is substantially planar and is slidably received in said housing means in snap-fit fashion.
 7. The needle holder of claim 6, wherein said end cap of said housing means includes an extended portion which is substantially congruent with said external element of said actuation means when said actuation means is in said initial position.
 8. The needle holder of claim 7, wherein each of said first and second threaded halves includes a top surface adjacent to said end cap of said housing means, and wherein engagement between said top surfaces of said threaded halves and the hub disk of the cannula hub limits further insertion of the cannula hub into said holder.
 9. The needle holder of claim 1 or claim 2, wherein the diameter of said threaded passageway defined by said first and second threaded surfaces is smaller than the diameters of both of said apertures in said end cap and said end wall, and wherein the perimeter of said threaded passageway does not subtend the perimeters of either of said apertures of said end cap and of said end wall when said threaded halves are in said cannula-mounting position.
 10. The needle holder of claim 5, wherein the diameter of said threaded passageway defined by said first and second threaded surfaces is smaller than the diameters of both of said apertures in said end cap and said end wall, and wherein the perimeter of said threaded passageway does not subtend the perimeters of either of said apertures of said end cap and of said end wall when said threaded halves are in said cannula-mounting position.
 11. A needle holder for use with a fluid collection and/or injection system of the type having a needle assembly and a fluid container, the needle assembly including a fluid passage bore extending therethrough and a hub, the fluid container including a fluid passage end and an opposing end, said needle holder comprising: a hollow body having an end wall at a closed first end thereof, said end wall having an aperture therethrough, said hollow body also having an open second end opposite to said first end for receiving a fluid container within said hollow body such that, upon reception of the fluid container, the fluid passage end of the fluid container is adjacent to said end wall; housing means abutting said first end of said hollow body for maintaining at least a portion of an actuation mechanism within said holder, said housing means including means defining an aperture therethrough which is generally coaxial with said aperture of said end wall; and an actuation mechanism for detachably mounting a cannula hub therein with one end of the cannula extending forwardly of said actuation mechanism for venipuncture and the other end extending rearwardly into said hollow body for engagement with the fluid container, said actuation mechanism including: first and second mounting jaws rotatably mounted within said housing means for removably mounting the cannula hub upon inserting the cannula hub into said actuation mechanism, said first and second mounting jaws being pivotable between a cannula-mounting position wherein said mounting jaws cooperate to define a passageway complementary in cross-sectional shape to the cross-sectional shape of the cannula hub, and a retracted position wherein said mounting jaws cooperate to define an opening having a cross-sectional size which is greater than the cross-sectional size of the cannula hub; a pivot axle for rotatably mounting said first and second mounting jaws within said housing means; and actuation means for urging said first and second mounting jaws between said cannula-mounting and retracted positions, said actuation means being slidably mounted to said housing means for linear reciprocal movement between an initial position wherein said first and second mounting jaws are urged into said cannula-mounting position, and a secondary position wherein said first and second mounting jaws are urged into said retracted position.
 12. The needle holder of claim 11 wherein said first and second mounting jaws comprise first and second threaded halves.
 13. The needle holder of claim 11 or claim 12, wherein each of said first and second mounting jaws further comprises a torque member; and wherein said actuation means comprises: a user-operable external element; and first and second arms extending from said external element, said first and second arms engaging respective torque members to urge said first and second mounting jaws into said retracted position in response to the application of linear force to said user-operable external element.
 14. The needle holder of claim 13, wherein said actuation means further comprises: resilient means for biasing said actuation means to said initial position wherein said first and second mounting jaws are urged into said cannula-mounting position by said first and second arms of said actuation means.
 15. The needle holder of claim 14, wherein said housing means further comprises: a bearing wall for opposing said resilient means of said actuator; and an end cap at one end of said holder for retaining at least a portion of said actuation mechanism within said housing means, wherein said end cap includes said means defining an aperture in said housing means.
 16. The needle holder of claim 15, wherein said end cap of said housing means is substantially planar and is slidably received in said housing means in snap-fit fashion.
 17. The needle holder of claim 16, wherein said end cap of said housing means includes an extended portion which is substantially congruent with said external element of said actuation means when said actuation means is in said initial position.
 18. The needle holder of claim 17, wherein each of said first and second mounting jaws includes a top surface adjacent to said end cap of said housing means, and wherein engagement between said top surfaces of said mounting jaws and a hub disk of the cannula hub limits insertion of the cannula hub into said holder.
 19. The needle holder of claim 11 or claim 12, wherein the diameter of said passageway defined by said first and second mounting jaws is smaller than the diameters of both of said apertures in said end cap and said end wall, and wherein the perimeter of said passageway does not subtend the perimeters of either of said apertures of said end cap and of said end wall when said mounting jaws are in said cannula-mounting position.
 20. The needle holder of claim 15, wherein the diameter of said passageway defined by said first and second mounting jaws is smaller than the diameters of both of said apertures in said end cap and said end wall, and wherein the perimeter of said passageway does not subtend the perimeters of either of said apertures of said end cap and of said end wall when said mounting jaws are in said cannula-mounting position.
 21. A holder for removably mounting an externally threaded needle assembly, said holder comprising: a hollow body having an open proximal end and a distal end closed by an end wall having an aperture therethrough; first and second threaded jaws mounted at the end wall; and an actuator assembly disposed at said distal end and comprising an actuator slidably mounted to said holder and operatively associated with at least one of said threaded jaws to move said at least one of said threaded jaws between a needle assembly mounting position in which said first and second threaded jaws cooperate to define a threaded passageway aligned with said aperture for receiving and securing such externally threaded needle assembly, and a needle assembly release position in which said passageway is sufficiently enlarged to free such externally threaded needle assembly from said holder.
 22. A holder for removably mounting an externally threaded needle assembly, said holder comprising: a hollow body having an open proximal end and a distal end closed by an end wall having an aperture therethrough; first and second threaded jaws mounted at the end wall; and an actuator slidably mounted to said holder at said distal end and operatively associated with at least one of said threaded jaws to move said at least one of said threaded jaws between a needle assembly mounting position in which said first and second jaws cooperate to define therebetween a threaded passageway having a first cross-sectional area and aligned with said aperture, and a needle assembly release position in which the threaded passageway has a second cross-sectional area which is larger than the first cross-sectional area.
 23. The holder of claim 21 or claim 22 wherein said actuator is integral with at least one of said threaded jaws.
 24. The holder of claim 21 or claim 22 wherein said needle assembly comprises a double-ended cannula.
 25. The holder of claim 24 further comprising an evacuated container having a puncturable membrane which is penetrated by one end of said double-ended cannula.
 26. The holder of claim 21 or claim 22 wherein at least one of said threaded jaws is slidable towards the other to position said jaws in the mounting position, and is slidable away from the other to position said jaws in the release position.
 27. The holder of claim 21 or claim 22 wherein at least one of said threaded jaws is dimensioned and configured to move slidably in a single plane between the needle assembly mounted position and the needle assembly release position.
 28. The holder of claim 27 wherein said actuator is dimensioned and configured to slidably move in a single plane.
 29. The holder of claim 21 or claim 22 wherein said actuator is dimensioned and configured to slidably move in a single plane.
 30. A method for mounting an externally threaded needle assembly to a holder and thereafter releasing the needle assembly therefrom, the holder having a distal end at which is disposed an actuator and first and second threaded jaws, at least one of which jaws is movable relative to the other, the first and second threaded jaws cooperating to form therebetween a threaded passageway, and the actuator being operatively associated with at least one of threaded jaws, the method comprising the steps of: securing a needle assembly into the threaded passageway; thereafter operating the actuator to slide at least one of the threaded jaws in a single plane away from the other threaded jaw to thereby sufficiently enlarge the threaded passageway to release the needle assembly from said holder.
 31. The method of claim 30 including operating the actuator by sliding it in the single plane.
 32. The method of claim 30 or claim 31 wherein the step of securing a needle assembly into the threaded passageway is carried out by operating the actuator to slide at least one of the threaded jaws away from the other threaded jaw to thereby sufficiently enlarge the threaded passageway to position the needle assembly therewithin, and then operating the actuator to slide at least one of the threaded jaws towards the other threaded jaw to engage the needle assembly within the passageway. 